Archive for the ‘Squid’ Category

Project Update

June 4, 2018

If one was not following the mailing lists it might seem the Squid project has gone the way of the Dodo. In truth it is quite the opposite. The dev team and Foundation board are working so hard it has been difficult to find time for these additional updates.


So to recap the major projects going on since last update;

The largest change has been our move to git for source code repository. That has been a long road taking up a lot of time over several years. A great big thanks to the various people working on that.

Following along from that we now have github (squid-cache account) as our code repository for public access. The Squid Projects repository is no longer directly available for general access. Our code submission process has changed from accepting .patch files to github PR requests. So developers working on code changes please convert to that (I can still work with patch submissions, but it is significantly more trouble than having your own github account for submission updates/edits). Anyone who forked one of the Squid github repositories prior to the 2017 transition should fork the new repository and convert their code changes.


The new code submission process has resolved quite a few issues we had with the old submit and auditing/QA process. There are still a few quirky behaviours caused by github and our automation that cause trouble from time to time – but overall it is a big improvement on what we had before.

The largest issue we face now for QA and code development is manpower. We now have automated change tracking, content integration helping out with QA and a committer bot taking a huge load off my shoulders as maintainer. Our submission process is open and public – so anyone can read the proposals and should also be able to comment about any bugs you can see that have not already been pointed out. Anyone with an interest in the Squid code is encouraged to participate in that process.


In the shadow of all those very time consuming alterations to the Squid Project systems the dev team has also managed to iron out several of the major bugs blocking Squid-4 release. Just one of the long-standing bugs remain. A few regressions in recent code have brought up some new major bugs, but those are for the most part already fixed or soon will be. So watch this space for news on further progress there.

Whats going on with Squid 4

July 1, 2016

Those that have been paying attention will have noticed that Squid-4 beta cycle has been going on for a very, very long time. A whole year now in fact. There are several reasons for this.

* The ecosystem that Squid is deployed into has a somewhat mixed situation in regards to C++11.

Even 5 years after it was standardized compiler support is still not readily available in some popular OS distributions. In particular there are a large number of people clinging to the outdated but still supported RHEL 6 and its derived family of OS which do not easily provide recent versions of GCC. So we are procrastinating on the deprecation of Squid-3.5 to give more people a chance to move on. The clock is ticking though.

* We had a lack of early adopters testing the early versions of Squid-4.

So bugs that only show up in real usage have been very slow to be found. We don’t make a new version start its beta cycle until the developers are reasonably sure that its stable enough to be used. The beta process is supposed to be just a confirmaton of that. Indeed a year ago 4.x looked like it had no bugs at all. Which is kind of suspicious, but not impossible. As the betas progressed though the bug reports started rolling in. It is somewhat a testament to how our modern build systems are catching out minor and trivial bugs that these tester reported issues have largely all been difficult to resolve.

* We are experimenting with a new management process for Squid releases.

Previously Squid-5 would have been branched for development and Squid-4 starting to stagnate, er, become “stable”. This time though we have delayed the branching and instead kept Squid-4 as main development branch for minor changes while the beta cycle goes on. That has made it a little more volatile than most of the Squid-3 series betas.

All up, we are down to the last few major bugs to be resolved in the new code. Progress on those is slow but steady. So Squid-4 production “stable” release should be not to far ahead on the calendar.

Squid-3.2 mythbusting NAT

December 19, 2014

One of the more frequently mentioned “problems” with Squid-3.2 since its release is a change in how it handles NAT failures.

The Myths

“Squid used to work when I NAT traffic to it from my router.”

“Squid used to work with one port when I configure the browser and NAT traffic.”

The Reality

No. Squid up until 3.1 would silence the NAT errors and treat the router as if it were the client browser. Any differences between the Host header and the requested URL were also completely ignored. All of this would be invisible to you the administrator, hidden at debug levels not normally shown. With several of the problems being completely unrecorded as well.

This last part seems to be behind a fair bit of skepticism about whether the problem we solved really exists. Nothing was showing up in the logs before and even a full packet trace from Squid or a gateway server would not reveal how JavaScript hijacks a client browser to pass internal documents to an external attacker.

What Changed?

Squid-3.2 finally added Host header validation to protect against the nasty behaviour and a few 0-day attacks using CVE-2009-0801 security vulnerability. Which has been a known flaw with NAT interception by HTTP proxies for at least 12 years now. This meant two things had to change:

* ignoring NAT errors had to stop. We can’t rely on validation results if the TCP details are already known to be corrupted.

* traffic directly from a browser to a NAT intercept port on Squid had to stop. There is no way to separate the NAT lookup result of error and unknown entry. A pity really, but that is what we are forced to work with.

During testing we uncovered a lot of really quite nasty behaviour by various clients, and indeed some public services setup to take advantage of the NAT bug as if it were a feature. On the whole a lot of client software sends a Host header with values strangely unrelated to what is being requested of the proxy. All of this had to go, or did it? for most of the year or so of testing it was banned completely and a HTTP error message returned for any such garbage. But in the end it was clear that we had to let it through somehow or we would be pitting Squid against the biggest players on the Internet … yeah.

(Almost-) Final Results

Squid-3.2 and later will reject traffic where NAT lookups fail on an intercept port. This includes NAT done on external devices and browsers directly sending proxy requests to the Squid intercept port. At the very least accurate reporting about the traffic and what it contains is the critical factor. If we let this traffic into Squid it would seriously compromise the validation results and also allow malicious clients to attack internal network resources with a large measure of anonymity. Neither of which is acceptible for a proxy trusted with controlling user traffic.

The best practice guideline for some years has been that NAT MUST be done on the Squid device. Squid-3.2 are now enforcing it as a basic requirement. If you are one of the network administrators running into this requirement change, please investigate the Policy Routing functionality of the device you originally had doing the NAT.

Squid-3.2 and later will accept invalid Host headers and produce a response to the client. But they will not cache the untrustworthy transaction results. They will contact the same server which the client TCP connection would have originally reached had Squid not been there (visible as ORIGINAL_DST in the logs). Notice that this is now deserving of the name “transparent proxy” a lot more than previous intercepting Squid. Even so NAT interception is still only half-transparent with the server being able to easily identify the proxies existence.

The loss of caching is intended to be a temporary solution until we can properly implement per-client caching of objects. As the saying goes there is nothing so permanent as the temporary – Squid still contains this workaround several series later. Support with this work is very welcome.

The situation when upstream peers are involved is also quite dangerous. For now we have had to permit Squid to pass the traffic to peers, which opens all multi-hop systems of proxies to the same vulnerabilities that were previously possible wth a single intercepting proxy. The solution is also going to require a substantial amount more work and be some years away. For the meanwhile it is a good idea to avoid passing intercepted traffic to cache_peer when possible.

More information on the problems, log entries, when they occur and what can be done about each is detailed in the Squid wiki Host header forgery page.

Zero-Sized Replies from Windows Servers

April 30, 2014

During the last few months there have again been a number of bug reports and queries from administrators seeing Zero Sized Reply error pages being produced by Squid 3.2 and later.

These “errors” are produced when Squid sends an HTTP request, then something out in the network goes wrong and the TCP connection gets severed while Squid is still waiting for the start of HTTP response to arrive. As you can imagine this is a little vague because that “something” is any one of a large set of potential networking problems.

Investigation of the old usual culprits in ECN, Window Scaling, PMTUd, and CONNECT proxying ruled them out leaving us mostly in the dark.

Testing without the proxy appeared to work fine. As did small short transactions even through the proxy. Leaving us more than a little confused.

The most common theme this time seems to be Windows based SSL/TLS services with recent but not top of the line software versions. IIS or Sharepoint on Server 2008 and 2010 for example.

Daniel Beschorner has done some investigating and reported this:

Since Squid 3.2 the SSL flag SSL_OP_ALL is no longer enabled by default in Squid. It enables different workarounds in the OpenSSL library.

Windows / IIS seems to get confused by empty packets (to mitigate the BEAST attack) sent from OpenSSL in TLS 1.0.

So the possibilities are:

We have also had remarkably similar problem reports about iTunes servers. That one is still unconfirmed and unresolved.

Happy Eyeballs

July 14, 2012

Geoff Huston wrote up a very interesting analysis of the RFC 6555 “Happy Eyeballs” features being added to web browsers recently.

As these features reach the mainstream stable browser releases and more people being using them Squid in the role of intercepting proxy are starting to face the same issues mentioned for CGN gateways. For all the same reasons. Whether or not you are operating an existing interception proxy or installing a new one this is one major new feature of the modern web which needs to be taken into account when provisioning the network and Squid socket/FD resources.

Squid operating as forward proxy do not face this issue as each browser only opens a limited number of connections to the proxy. Although Firefox implementation of the  “Happy Eyeballs” algorithm appears to have been instrumental in uncovering a certain major bug in Squids new connection handling recently.

A Squid Implementation

For those interested, Squid-3.2 does implement by default a variation of the “Happy Eyeballs” algorithm.

DNS lookups are performed in parallel now, as opposed to serial as they were in 3.1. As a result the maximum DNS lookup time is reduced from the sum of A and AAAA response times, to the maximum of both.

TCP connection attempts are still run in serial, but where older versions of Squid interspersed a DNS lookup with each set of TCP attempts the new 3.2 code identifies all the possible destinations first and tries each individual address until a working connection is found. Retries under the new version are also now limited per-address where in the older versions each retry meant a full DNS result set of addresses was re-tried.

As a result dns_timout is separated from connect_timeout which is now fully controlling only one individual TCP connection handshake.

Proxying HTTPS for an internal service

June 18, 2011

Since version 2.6 changed the way http_port worked and let Squid service multiple different types of traffic simultaneously people have been struggling with one setup which should to all outward appearances be quite simple.

I’m speaking of the scenario where you have a proxy serving as both a forward-proxy gateway for the internal LAN users and as a reverse-proxy gateway for some SSL secured internal services (an HTTPS internal site).

Both setups are essentially simple. For the reverse-proxy you setup an origin cache_peer with SSL certificate options. Perhapse an https_port to receive external traffic.  For the forward-proxy you setup users browsers to contact the proxy for their HTTP and HTTPS requests. Perhapse with NAT interception to force those who refuse.

They you discover that Squid can’t seem to relay requests from internal users to your internal peer. You get warnings about clientNegotiateSSL failing on plain HTTP requests. Even though it may appear the user was opening HTTPS properly to contact it.

The problem is that when relaying through a known proxy browser wrap their SSL request, inside a CONNECT tunnel setup request. Which is plain-text HTTP. Squid passes this intact on to any cache_peers you have configured. Even the origin one which is expecting SSL. It may do the right thing and wrap it in a second layer of SSL. But that just makes things worse as the server at the other end gets this weird CONNECT request it cant do anything with.

Until recently the only fix has been to setup a bypass so that internal LAN users don’t use the proxy when visiting the internal HTTPS site. Which works perfectly for user access. But does cause problems on the recording and accounting systems which now have to track two sets of logs and filter proxy relayed requests out of one.

Or alternatively to set the LAN DNS to point users at the reverse-proxy port and figure some way to avoid forwarding loops by bypassing Squid like above or disabling the loop detection.

Both alternatives having the same problems at best. Worst case in the second you have opened some security vulnerabilities by ignoring loops.

In Squid-3.1 we have trialled two possible ways to fix this whole situation.

The first attempt was to simply not relay CONNECT to peers with origin type configured. This failed with a few unwanted side effects. One was that Squid would lookup the DNS and go to that server. Fine for most, but not all Squid have split-DNS available. Or Squid could relay it to a non-origin peer instead. Possibly halfway round the world with worse lag effects than a little extra calculation handling the logs.

The second attempt, which we are currently running with in 3.1.12 and later. Is to strip the CONNECT header and connect the tunnel straight to the peer. But only when the peer port matches the intended destination of that tunnel, and your access controls permit it for selection.

  • The port restriction is there as a simple check that the service is likely to match protocols. Even if we cant be sure which.
  • Traffic to that internal service does go through the proxy and traffic accounting only has to handle the proxy logs.
  •  Requests from LAN clients use the clients SSL certificates instead of the cache_peer configured ones.

This last point is one which can bite or confuse. If you have LAN users in this type of scenario and require all contact with the internal service to use the proxy configured certificates you will still need to configure those clients with the old methods.


Enjoy. And as always, if you have better ideas or problems please let us know.

Project Update: Bugs, bugs, betas and breakages

October 24, 2010

So much for a monthly update with hints and tips. Been a year and more! So I guess this post should start again by covering what has been going on over this past year. “Not much and far too much” just about covers it …


Bugs …

Business as usual has seen a steady parade of upgrades from earlier versions up to 3.0 and 3.1. Bringing with it a steady stream of bug reports for all sorts of varied things overlooked or not yet fixed. The increasing number of reports people are giving of old bugs that have annoyed them without being reported is pleasing in a way. I hope this means less overall and display stuff is relatively easy

Some people have had shocks; bugs reported over a year ago being fixed suddenly and some new reports not lasting the day. I can’t stress enough how important your help in researching the problems is.

The oldest bugs are simple “Squid is doing X”. Um, yeah well, we can assume what the expected behaviour was (sometimes). After prodding (a day or so later) up comes a version number and build options.

For example; I was looking at a typical old bug today. Still open from 2007 that never got any further than build options and behaviour description despite several requests for more info.  One day somebody is going to have to setup several machines build 3.0 a couple of times with multiple features on or off and try to replicate the described problem.  Then build 3.HEAD and try to replicate X all over again starting with the same tests. Then try to figure out how its happening and whether a fix might be possible.  Well, thanks for the report anyway, at least we know to watch for it meanwhile.

Every few months like today, I trawl through these, just over 100 bugs now, looking for ones which I could maybe replicate in less than a few days. Today I’m slightly happy. One died as invalid, and two died as no longer fixable. The whole area of code they might have been in is dead.


… bugs …

The shorted lived bugs by comparison, are reports that version a.b.c. is doing X when it should be doing Y. They include in the case of crashes and segmentation faults a backtrace of the code (with symbol names). They include header or packet traces if the problem was communicating to some other software. Some even came with information tracking down which feature and piece of the code was going wrong. Found, tracked, patched, tested, and fixed in the main code in mere hours of work.  A HUGE thank you to everyone who reports bugs like this.


… betas …

Squid-3.2 has started its beta releases this year. Following the fluffy “grand plan” of being a bit more predictable:  branch in Jun with monthly betas through until a stable series probably appears Dec or Jan.

The fluffy part is caused by some more structural cleanup projects we really really want to make the code easier to work with. Well, late Oct and about half of the cleanups have been done. The stable part is today looking more like next Jan/Feb provided the rest are done and working soon.

Another post closer to 3.2 stable release will cover whats going on there in the features. Some cool stuff. If you want a sneak preview the release notes are already available.


… and breakages.

Ah, well. Some may recall and friends. The background there for the inquisitive is that two feature changes clashed head-on and killed stability for two months.

I have irregular but available contact with nine of the maintainers packaging Squid for popular systems. It started slowly, growing until half of them had informed me that important sections of their users were being hit by the lack of IPv6 split-stack support in 3.1.

It surprised me a bit how many people and what in situations are insisting that IPv6 be turned off, but only partially. This was a big problem for early 3.1 series since the build process actively probed IPv6 capabilities and turned various capabilities on or off inside Squid. So an essentially simple change was made, moving the active testing into Squid startup process. Squid builds with IPv6 anywhere and runs it when available. No such luck on simple, enter all the little quiet bits assuming IPv4-only or IPv6-only sockets.

The other feature change that made the recovery even messier was a version bump to libtool in our package bundling system. In short a very simple basic upgrade omission on our part broke the tarball package. A veritable storm of hacks appeared to work around the broken tarballs and extended the fix time as testers disappeared with “it works for me now” leaving the systemic problem unresolved.

3.1.8 finally got some pedantic methodical testing before release and a fix for both problems.


Background to all this drama we have had an increase in focus on HTTP/1.1 support over the year from The Measurement Factory. Many of the minor behaviour bug fixes made it into the 3.1 series and the last of the big changes being held back to 3.2.

Continuous Integration

August 18, 2009

For the last few years there has been a slow growing improvement to the testing and QA Squid is subject to. This last week has seen the construction and rollout  of a full-scale build farm to replace some of our simple internal testing. Robert Collins covers the growth process in his blog.

Here is the initial release notice:

Hi, a few of us dev’s have been working on getting a build-test environment up and running. We’re still doing fine tuning on it but the basic facility is working.

We’d love it if users of squid, both individuals and corporates, would consider contributing a test machine to the buildfarm.

The build farm is at with docs about it at

What we’d like is to have enough machines that are available to run test builds, that we can avoid having last-minute scrambles to fix things at releases.

If you have some spare bandwidth and CPU cycles you can easily volunteer.

We don’t need test slaves to be on all the time – if they aren’t on they won’t run tests, but they will when the come on. We’d prefer machines that are always on over some-times on.

We only do test builds on volunteer machines after a ‘master’ job has passed on the main server. This avoids using resources up when something is clearly busted in the main source code.

Each version of squid we test takes about 150MB on disk when idle, and when a test is going on up to twice that (because of the build test scripts).

We currently test:

  • 2.HEAD
  • 3.0
  • 3.1
  • 3.HEAD

I suspect we’ll add 2.7 to that list. So I guess we’ll use abut 750MB of disk if a given slave is testing all those versions.

Hudson, our build test software, can balance out the machines though – if we have two identical platforms they will each get some of the builds to test.

So, if your favorite operating system is not currently represented in the build farm, please let us know – drop a mail here or to noc @ – we’ll be delighted to hear from you, and it will help ensure that squid is building well on your OS!


That just about covers everything. Hardware and build software requirements are listed in the build farm page.

Hi, a few of us dev's have been working on getting a build-test
environment up and running. We're still doing fine tuning on it but the
basic facility is working.

We'd love it if users of squid, both individuals and corporates, would
consider contributing a test machine to the buildfarm.

The build farm is at with docs about it at

What we'd like is to have enough machines that are available to run test
builds, that we can avoid having last-minute scrambles to fix things at

If you have some spare bandwidth and CPU cycles you can easily

We don't need test slaves to be on all the time - if they aren't on they
won't run tests, but they will when the come on. We'd prefer machines
that are always on over some-times on.

We only do test builds on volunteer machines after a 'master' job has
passed on the main server. This avoids using resources up when something
is clearly busted in the main source code.

Each version of squid we test takes about 150MB on disk when idle, and
when a test is going on up to twice that (because of the build test

We currently test

and I suspect we'll add 2.7 to that list. So I guess we'll use abut
750MB of disk if a given slave is testing all those versions.

Hudson, our build test software, can balance out the machines though -
if we have two identical platforms they will each get some of the builds
to test.

So, if your favorite operating system is not currently represented in
the build farm, please let us know - drop a mail here or to noc @ - we'll be delighted to hear from you, and it will help
ensure that squid is building well on your OS!


Life of a Beta

July 11, 2009

From early inception when the developers have nothing but dreams for it.  Through the coding and arguments about what should be included and how. Through the alpha testing with its harrowing hours pondering obscure code from last decade. Even the odd period of panic as security bugs are whispered about behind closed doors. Such is the early life of software.

Two weeks ago word went out that 3.1 was reaching end-game.

This part of the release lifecycle seems to be going well. Packages appearing very slowly as QA throws demanding eyes on the code and making us actually fix things. Don’t be fooled by the packages out already, they have been in QA for a few months to get this far. On that note:

NetBSD, Gentoo, Ubuntu, FreeBSD and RedHat already have packages ready and available for at least testing use if you know where to look (ie the links right there might be a good start).

Debian has a bit more QA to go as of the writing, but the maintainer tells me there will be packages out soon.

OpenBSD and Mac turned out at the last minute to be running split-stack IPv6 implementations (for security apparently). All the documentation read in two years left the impression it was a Windows XP anarchism (and who runs XP Pro on a server?), so support was delayed and delayed.  The OpenBSD maintainer and someone interested from Mac are working with myself on closing that gap in the features.

There may be more OS with 3.1 packages. I’ve only begun working my way down the popularity list to see which OS do and who to contact. Squid has bundles on over 600 OS apparently.

If you know who does the official packaging for your OS and whether there are 3.1 packages ready, please do me a favor and mention it. I’m seeking a web page where to find the squid (or squid3/squid30/squid31) package information and also the place where distro bug reports about Squid might end up.

What is holding 3.1 back?

March 17, 2009

One of the major changes we made to 3.1 during its life cycle was the introduction of first-past-the-post feature additions instead of pre-planned and sealed roadmaps. Combined with a regular short release timeline instead of indeterminate long testing periods.

So why has 3.1 taken more beta releases than 3.0?

Unfortunately before that policy was implemented we did go down the old track a fair way and guaranteed that several features would make it into 3.1.  One of these (SourceLayout) has proven to be a lot of slow work. (Not major re-writing thankfully).

The other new features code for 3.1 have been tested and stabilized between and and are happily in use on many production environments.  But this last remaining feature still has a lot to go in and be tested for bugs. The result is 6 months delay on 3.1 and a handful of extra candidate releases, even some blockage of new stuff ready to go into 3.HEAD for the next release.

3.2 is starting off without this old legacy blocking problem, so it should be the first release to really gain the benefit of a much faster testing and release stages of production.

There are also a bunch of bugs which seem to be important but we are unable to track down and fix yet. Mostly holdovers from 3.0. The basic policy is to block release until all open bugs major or higher are closed. We might downgrade bugs to normal though if they are voted to be ignored.

While we wait for the last feature to stabilize some of us still try to work away at that list, additional volunteers are very welcome to speed things up.  Meanwhile I would like some opinions please about the final stage for 3.1: